Grain oriented silicon steel containing selenium and method of making the same



Nov. 17, 1964 rrsuo IMAl ETAL 3,157,538

GRAIN ORIENTED SILICON STEEL CONTAINING SELENIUM AND METHOD OF MAKING THE SAME Filed Dec. 12. 1960 2 Sheets-Sheet 1 ]N VEN TOR.

United States Patent lan GRAIN GRIENTED SILHZQN STEEL CGNTAWENG SELENIUM AND lvi 'ildfil) 8F MAKENG THE SAlvlE Mitsuo lmai, Hyogo-ku, Kobe, Tatsuo Nakayama, Tokarazuka, lsamn Soto and Hiroshi Shimanalra, Ashiya, Kazuo Tsurnoka, Some-kn, Kobe, isao M atoha, Ashiya, Yutaka Ono, Nada-ion, Kone, and Akin Ramada, Higashi-Nadadru, Kobe, Japan, assignors to Kawasaki Steel Corporation, Kohe-shi, Japan Filed Dec. 12, 196i Ser. No. 75,435 \Claims priority, application Japan May 17, 1960 Claims. (til. 143-412) This invention relates to improvements in silicon steel having a very high degree of preferred orientation. More particularly, it relates to a method of grain oriented silicon steel containing 0.001 to 0.100 percent selenium.

In general, the grain oriented silicon steel has a crystal orientation known as so-called Goss orientation or cubeon-edge orientation, in which the (110) plane of the crystal is parallel to the rolling plane and the [001] direction lies parallel to the rolling direction. When such a material is magnetized in parallel with the rolling direction, high permeability and low core loss which are most suitable for constructing transformer cores may be obtained, since the [001] axis is the easy direction of magnetization.

Many methods of producing grain oriented silicon steel have been proposed in several countries. However, most of them relate to conditions on which the material is rolled and heat treated in the stage of cold rolling. For instance, an ingot of silicon steel containing about 3 percent silicon is bloomed into a slab which is further hot rolled into a strip having a suitable thickness. Then this strip is subjected to two stages of cold rolling with an intermediate annealing to produce a cold rolled strip having a desired final thickness.

In the process above described, there are two kinds of methods in the cold rolling stage. In accordance with one process proposed by N. P. Goss in US. Patent No. 1,965,- 559, the strip is cold reduced at least 50 percent for each of the two stages of cold rolling. In accordance with another process stated by I. M. Jackson in US. Fatent No. 2,535,420, at the first stage the strip is cold reduced as high as 80 percent, and at the second stage the reduction of about 2 percent is applied. The strip reduced to the find thickness by either method is annealed at an el vated temperature of at lowest 1100 C. so as to develop the preferred orientation to full extent. Both methods above mentioned comprise many complicated steps from an ingot to a sheet or strip of final gauge, so that much attention must be paid to insure the quality of the final product. As even a slight variation in the rolling and heat treatin conditions influences remarkably on the magnetic properties of the final product, sometimes it results in unexpectedly deten'ous properties.

Formerly it was recognized that the impurities should be kept as low as possible for ensuring the good magnetic properties. On the other hand it has been found that the desired texture in the final product is remarkably improved indirectly by addition of some kinds of elements, once considered as impurities, having a serious efifect upon the behaviour during secondary recrystallization. For instance, J. D. Fast disclosed in US. Patent No. 2,802,761 and I. B. May disclosed in U.S. Patent No. 2,867,55 8 that, by addition of nitrogen and sulphur, Goss texture in final product had been well developed owing to the inhibition of growth of undesirably oriented grains during recrystallization, and the instability of the quality from a slight variation in rolling and heat treating conditions may be avoided.

In the course of the experiments with regard to the impurities or additional elements in silicon steel, we have discovered that selenium addition is very eflective upon the development of the desired texture. The features of this invention result in not only the improvements of magnetic properties, but also the stability irrespective of the variations of the processing.

Briefly stating the aspect of this invention, the method is a process of producing grain oriented silicon steel comprising steps of adding 0.001 to 0.100 percent by weight of selenium in the form of ferroselenium or metallic selenium into molten silicon steel containing 2 to 4 percent by weight of silicon for casting an ingot, and treating said ingot by ordinary methods. By virtue of this process, the product having well developed texture of the Goss orientation, low core loss, high permeability, and uniformity of properties throughout the strip, may be obtained in spite of some variations in conditions of hot rolling, cold rolling, and heat treatment.

These and other features of our invention will appear from the description in connection with the accompanying drawings, in which FIG. 1 is a macrostructure of grain oriented silicon steel fully treated in accordance with this invention;

FIG. 2 is the pole-figure as determined by X-ray dihraction method of the same steel after final annealing;

FIG. 3 is a graphical illustration of magnetic torque curve of such a grain oriented silicon steel after final annealing; and

FIG. 4 is a graphical illustration of distribution of magnetic flux density of materials containing different kinds of additional elements produced by conventional process.

Referring now to the drawings, embodiments of this invention will be explained. Molten silicon steel was refined in open-hearth furnace so as to reduce the contents of harmful impurities to a sulficiently low extent, and it was poured into ingot molds. On casting the above mentioned ingots, metallic selenium was added to the molten steel so as to obtain a series of ingots containing various contents of from 0.001 to 0.100 percent of selenium. The ingots of about 6,000 kg. by weight were heated in soaking pits sufficiently and then bloomed into slabs of 127 mm. in thickness which were heated again and then hot rolled into strips of 2.0 to 2.4 mm. in thickness. After annealing and pickling, the strips were cold reduced to thickness of 0.30 or 0.35 mm. with an intermediate annealing, which were finally subjected to annealing at an elevated temperature of about 1150 C.

Experimental results of the grain oriented silicon steel containing selenium subjected to the process in accordance with this invention will be explained by following example. FIG. 1 illustrates a macrostructure of such a sample in which coarse crystal grains have grown selectively by secondary recrystallization. FIG. 2 is the (100) pole-figure as determined by X-ray diffraction technique about the twenty crystal grains selected at random from the specimen shown in FIG. 1. It illustrates that the crystal grains after secondary recrystallization locate near by the [001] orientation or the Goss orientation. FIG. 3 shows the magnetic torque curves in-which solid line represents that of the specimen processed according to our invention, and broken line that of a single crystal of 3 percent silicon steel of the Goss orientation. It is understood that the development of the Goss texture in the specimen is estimated as about 90 percent from calculating the peak value ratio qualitatively. The mag-' netic properties are extremely improved as a result of such a development of the Goss texture in the specimen. This fact is apparent from Table l in which the magnetic properties of several samples containing difier'e'nt amounts of selenium are compared with those of ordinarily treated samples. Grain oriented silicon steel containing selenium has a superior quality such as lower core loss, higher permeability, and larger magnetic torque than ordinary steel.

TABLE 1 Magnetic Properties of Grain Oriented Silicon Steel Containing Selenium M aximum M agnetic Torque (dyne-crn cmfl) Addition of Selenium (wt. Percent) Core Loss W15/50 (W .llig.)

Permea- No. of Ingot bility 16. 6X10 14. X10 l5. 8X10 None INOONJOUIOM Furthermore, the effect of the present invention is apparent from FIG. 4 showing distribution ofmagnetic flux density of materials containing different additional elements. There were three kinds of additional elements; the first is without any addition, the second is sulphur proposed by I. E. May, and the third is selenium according to the present invention, each of which is refined so as to reduce all impurities to the lowest possible value before the addition. FIG. 4 illustrates the distribution of magnetic flux density at 10 oersteds in magnetizing force as measured from more than 100 specimens of test coils processed from the different kinds of ingots as above, having been subjected to the same rolling and heat treatment as in the preceding examples. As shown in FIG. 4, the magnetic flux density at 10 oersteds in magnertizing force as to most of the test coils without any addition lies between 17,000 and 18,000 gausses. When sulphur is added, almost all fall between 17,000 and 18,500 gausses while an appreciable part (about 40%) falls between 18,000 and 18,500 gausses. Now such test pieces containing selenium in accordance with this invention have magnetic flux density between 18,000 and 18,500 gausses more frequently (about 70%) and above 18,500 gausses to a slight extent. Thus the balance (about 25%) is between 17,000 and 18,000 gausses and none below 17,000 gausses at all. This result also suggests the selective growth of the grains in the Goss orientation and accordingly the improvement in the magnetic properties of the grain oriented silicon steel in accordance with this invention. It is possible to consider that the magnetic flux density at 10 oersteds in magnetizing force is not only a measure of the preferred orientation but also a criterion whether it is possible to lower the exciting current and to reduce the weight of the cores and windings for trans-' former design. Generally, it is considered that permeability above 1750 is classified as the highest grade of commercial product and permeabality above 1800 is called as exceptional.

According to above description, it is remarkable to improve the magnetic properties of silicon steel by this invention and it is considered that a range of 0.001 to 0.100 percent of selenium as an additional element would be eifective.

We should pay attention to the fact that the selenium added to the steel ingot might remain in the final product, because it might possibly increase the core loss in the final product. The amount of selenium added into the steel ingot does not increase during heating for blooming and hot rolling, and during intermediate heat treatment between cold rolling operations. Therefore, it is considered that the selenium in steel should be removed sutficiently during the final annealing at an elevated temperature. For this purpose it is preferred to anneal at an elevated temperature above 1000 C. in a reducing gas atmosphere such as hydrogen.

The reason why selenium added to silicon steel in ac cordance with this invention bringse the favourable results is not sufiiciently clear, but it is considered that selenium existing during the processing may control the grain size of the matrix and permit to expand the critical range of annealing temperature, annealing time, and rolling condition. It is also considered that fine dispersed phase formed by selenium in steel may have an effect for inhibiting the growth of crystal grains other than the Goss orientation during secondary recrystallization. It is sup Although we have shown and described certain specific embodiments of our invention, we are fully aware that many modifications may be made in our invention without departing from the spirit of it. Our invention, therefore, is not to be restricted except insofar as it necessitated by the prior art or by the spirit of the appended claims. 7

What is claimed as new and desired to be secured by Letters Patent of the United States is: a

1. The process of producing grain oriented silicon steel comprising the steps of adding 0.001 to 0.100 percent by weight of selenium into molten silicon steel so as to form a silicon steel composition consisting essentlally of 2 to 4 percent by weight of silicon, 0.001 to 0.100

percent by Weight selenium, the balance being iron, for, casing an ingot, and hot Working said ingot to a hot rolled strip, and subjecting said strip to at least one cold rolling treatment and final high temperature anneal.

2. The process of producing grain oriented silicon steel comprising the steps of treating said silicon steel to re-- duce impurities normally found therein, adding 0.001 to 0.100 percent by weight of selenium in the form of ferro selenium into said molten silicon steel so as to form a silicon steel composition consisting essentially of 2 to 4 percent by weight of silicon, 0.001 to 0.100 percent by weight seleniurmthe balance being iron, for casting an ingot, and hot working said ingot to a hot rolled strip, and subjecting said strip to at least one cold rolling treatment and final high temperature anneal.

3. The process of producing grain oriented silicon steel which comprises the steps of treating said silicon steel to reduce impurities normally found therein, adding 0.001

to 0.100 percent by weight of selenium in the form of metallic selenium to said silicon steel in the molten state so as to form a composition consisting essentially of 2 to 4 percent by weight of silicon, 0.001 to 0.100 percent by weight of selenium, the balance being iron, for easting an ingot, and hot working said ingot to a hot roll strip, and subjecting said strip to at least one cold rolling treatment and final high temperature anneal.

4. The process of producing grain oriented silicon steel comprising the steps of treating said silicon steel to reduce impurities normally found therein, adding 0.001 to 0.100 percent by weight of selenium to said thus treated silicon steel in a molten state so as to form a silicon steel composition consisting essentially of 2 to 4 5 percent by weight of silicon, 0.001 to 0.100 percent by weight of selenium, the balance being iron, for casting an ingot, and hot working said ingot to a hot rolled strip and subjecting said strip to at least one cold rolling treatment and final high temperature anneal.

5. Grain oriented silicon steel which consists essentially of 2 to 4 percent by weight of silicon, 0.001 to 0.100 percent by weight of selenium, the balance being 1ron.

References Cited in the file of this patent UNITED STATES PATENTS Dempster Mar. 29, 1 910 May Ian. 6, 1959 

1. THE PROCESS OF PRODUCING GRAIN ORIENTED SILICON STEEL COMPRISING THE STEPS OF ADDING 0.001 TO 0.100 PERCENT BY WEIGHT OF SELENIUM INTO MOLTEN SILICON STELL SO AS TO FORM A SILOCON STEEL COMPOSITION CONSISTING ESSENTIALLY OF 2 TO 4 PERCENT BY WEIGHT OF SILICON, 0.001 TO 0.100 PERCENT BY WEIGHT SELENIUM, THE BALANCE BEING IRON, FOR CASING AN INGOT, AND HOT WORKING SAID INGOT TO A HOT ROLLED STRIP,AND SUBJECTING SAID STRIP TO AT LEAST ONE COLD ROLLING TREATMENT AND FINAL HIGH TEMPERATURE ANNEAL. 